(1) Field of the Invention
The present invention relates to a resin composition for use in a coating composition, particularly useful for the application to the topcoating.
(2) Description of the Background Art
Outdoor applications, for example, topcoating films applied onto the bodies of automobiles, rail road cars, etc. had such disadvantages that the coating films showed poor appearance with time due to dust, sand dust, iron powder, acid rain, etc. in the air, particularly so for a coating film showing poor resistance to acid rain. For the purpose of solving the above disadvantages, attempts have been made on selection of a crosslinked resin and on improvements in physical properties of the coating film. However the above attempts all produced such problems that adhesion of pollutants onto the surface of the coating film makes it difficult to remove the resulting stain, resulting in showing poor film appearance.
As a method of preventing adhesion of pollutants onto the coating film, for example, a method of adding to a coating composition or coating onto the surface of the coating film an antistatic agent, which reduces a surface resistivity of the coating film so as to prevent a static adhesion of dust, etc. However, according to the above methods, poor water resistance of the conventional antistatic agent made difficult the maintenance of their effects in outdoor applications.
Japanese Patent Application Laid-Open No. 306328/94 discloses an acid rain-resistant coating composition prepared by adding a condensation product between an alkylsilicate oligomer and a silane coupling agent consisting of a hydrolyzate of an epoxy-functional silane to a coating composition, resulting in showing poor film performances.
For the purpose of preventing adhesion of pollutants by developing hydrophilic properties on the surface of a coating film while maintaining good film performances, a coating composition containing, as a hydrophilic properties-imparting component, a silicone compound having a specified organofunctional group and alkoxysilyl group is disclosed, for example, in Japanese Patent Application Laid-Open Nos. 40907/97, 40908/97, 40911/97, etc. The above coating composition makes it possible to form a coating film having hydrophilic properties on its surface and showing good properties in pollution resistance, acid resistance, etc. However, unsatisfactory compatibility of the base resin in the coating composition with the above silicone compound may cause the silicone compound to locally agglomerate, particularly the application to a cold-drying clear coating composition may form a clear coating film showing cloudiness, resulting in making difficult coexistence of finish properties with pollution resistance. Moreover, development of hydrophilic properties on the surface of the coating film during outdoor exposure required 3 months or longer, the development of hydrophilic properties from the beginning being demanded.